Systems and Methods for Gravitational Load Support

ABSTRACT

A load support device includes a first link coupled to a load. A second link is configured to couple to footwear. The second link is pivotally coupled to the first link. The first and second link comprise a link assembly. A first compliant member is disposed between the load and the second link. The first compliant member includes a tension spring or a compression spring. The link assembly further includes a tension cable coupled to the first compliant member. A first actuator is coupled to the first compliant member to control a stiffness of the first compliant member. A sensor is configured to couple to a user to measure a physical state of the user. A control system controls the first actuator based on a gait activity. The first actuator is actuated based on the physical state of the user. The load support device is tuned based on the load.

CLAIM TO DOMESTIC PRIORITY

The present application claims the benefit of U.S. Provisional Application No. 61/790,970, filed Mar. 15, 2013, which application is incorporated herein by reference.

FIELD OF THE INVENTION

The present invention relates in general to load support systems and particularly gravitational load support systems that allow for substantially unencumbered gait.

BACKGROUND OF THE INVENTION

Carrying significant loads over long distances and periods can lead to fatigue and cause musculoskeletal related injuries. Although various types of jobs require persons to carry loads, military personnel are considered particularly at risk for fatigue and injury. As the quantity and complexity of gear has increased, the weight of loads carried by military personnel has increased. For adequate preparation, many soldiers carry a variety of devices, which may include night goggles, global positioning systems (GPS), body armor, and other gear. Although maximum loads are recommended, the recommended maximums are typically exceeded.

Fatigue has been shown to have detrimental effects on individuals who carry the heavy loads. Fatigue is known to increase likelihood of injury by raising the potential for trips and falls. Fatigue can also impact mental focus, reduce situational awareness, and affect overall performance. Non-combat related injuries, caused by carrying significant loads, are also a concern.

Various types of structures have been proposed to lessen loads carried and prevent musculoskeletal injuries. Current load assistance structures are known to perturb the user's gait and negatively affect metabolic efficiency. Interference with gait creates inefficiencies in energy transfer, by altering fluidity of motion, which in turn increases metabolic cost and reduces metabolic efficiency.

SUMMARY OF THE INVENTION

A need exists for a load support system that assists users in carrying heavy loads and that allows for substantially unencumbered gait. Accordingly, in one embodiment, the present invention is a method of making a load support device comprising the steps of providing a first link coupled to a load and providing a second link configured to couple to a footwear. The second link is pivotally coupled to the first link. The method further includes the steps of disposing a first compliant member between the load and the second link, coupling a first actuator to the first compliant member to control a stiffness of the first compliant member, and providing a control system to control the first actuator based on a gait activity.

In another embodiment, the present invention is a method of making a load support device comprising the steps of providing a first link coupled to a load, and providing a second link configured to couple to a footwear. The second link pivotally coupled to the first link. The method further includes the steps of disposing a first compliant member between the load and the second link, and coupling a first actuator to the first compliant member to control a stiffness of the first compliant member.

In another embodiment, the present invention is a load support device comprising a first link configured to couple to a load. A second link is configured to couple to a footwear and the first link. A first compliant member is disposed between the load and the second link. A first actuator is coupled to the first compliant member to control a stiffness of the first compliant member.

In another embodiment, the present invention is a load support device comprising a link assembly configured to couple to a load and to a footwear. A first compliant member is coupled to the link assembly between the load and the footwear. An actuator is coupled between the load and the footwear, the first compliant member and actuator configured to dissipate the load during gait.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 illustrates a gravitational load support system worn by a user;

FIGS. 2 a-2 d illustrate a schematic diagram of a gravitational load support system;

FIGS. 3 a-3 c illustrate the effect of a load and a gravitational load support system on a user's posture and gait;

FIG. 4 illustrates a tension spring-based actuator used for a gravitational load support system;

FIGS. 5 a-5 b illustrate schematic diagrams of coils in a spring-based actuator used for a gravitational load support system;

FIG. 6 illustrates a graph of a spring-based actuator control pattern;

FIGS. 7 a-7 b illustrate a graph of kinematic results measured from a user wearing a gravitational load support system;

FIG. 8 illustrates a schematic diagram of alternative load support systems; and

FIGS. 9 a-9 d illustrate a graph of the relationship of motor power consumption to percentage of a gait cycle during use of a gravitational load support system.

DETAILED DESCRIPTION OF THE DRAWINGS

The present invention is described in one or more embodiments in the following description with reference to the figures, in which like numerals represent the same or similar elements. While the invention is described in terms of the best mode for achieving the invention's objectives, those skilled in the art will appreciate that the description is intended to cover alternatives, modifications, and equivalents as may be included within the spirit and scope of the invention as defined by the appended claims and their equivalents as supported by the following disclosure and drawings.

Human locomotion, such as walking and running, is commonly described in terms of gait. Gait is a cyclical or reoccurring pattern of leg and foot movement, rotations, and torques that creates locomotion. Due to the repetitive nature of gait, gait is typically analyzed in terms of percentages of a gait cycle. A gait cycle is defined for a single leg beginning with the initial contact of the foot with a surface such as the ground. The initial contact of the foot on the ground is referred to as a heel strike. The conclusion of a gait cycle occurs when the same foot makes a second heel strike. A gait cycle can be divided into two phases: stance phase and swing phase. Stance phase describes the part of the gait cycle where the foot is in contact with the ground. Stance phase begins with heel strike and ends when the toe of the same foot leaves the ground. Swing phase describes the part of the gait cycle where the foot is in the air and not in contact with the ground. Swing phase begins when the foot leaves contact with the ground and ends with the heel strike of the same foot. For walking gait speed, stance phase typically describes the first 60% of the gait cycle, while swing phase describes the remaining 40% of the gait cycle.

FIG. 1 shows a gravitational load support system 10 worn by user 12. User 12 carries a load 14 using a backpack 16 worn on an upper torso 18 of user 12. Backpack 16 couples to user 12 by straps 20, which rest on the user's shoulder area 22. Straps 20 represent an attachment point of load 14 to user 12. As user 12 walks, user 12 experiences forces from the weight of load 14 at the attachment points, such as shoulder area 22. Gravitational load support system 10, or load support system 10, allows weight from load 14 to bypass the user by absorbing and transmitting the weight into the user's footwear 26 and into the ground.

Gravitational load support system 10 includes a system of linkages that transmits load 14 worn on upper torso 18 to footwear 26 worn on the user's feet 28. Load support system 10 couples to load 14 and footwear 26. As user 12 walks, load support system 10 transfers the gravitational load 14 from upper torso 18 into footwear 26. Load support system 10 couples to load 14 at a load receptor point 30. In one embodiment, load support system 10 includes a load receptor point 30 coupled to backpack 16 or to a frame of backpack 16.

Load support system 10 further couples to a load transmission point 32. In one embodiment, load support system 10 includes a load transmission point 32 coupled to footwear 26 and footwear attachment 34. By coupling load support system 10 to backpack 16 and footwear 26, donning and doffing of load support system 10 is simplified for user 12. Load support system 10 is thus disposed between load receptor point 30 and load transmission point 32 to transmit the gravitational load 14 to load transmission point 32. Load support system 10 further includes a load receptor point 30 and a load transmission point 32 on each side of user 12 or load 14. Thus, a load transmission point 32 is coupled to footwear 26 on each of the user's feet 28.

Load support system 10 includes an upper link 40 and a lower link 42 positioned on each side of load 14. In one embodiment, load support system 10 includes at least four linkages: one upper link 40 and one lower link 42 on each side of user 12. Upper link 40 couples to backpack 16 at load receptor point 30. Upper link 40 couples to lower link 42 at one or more joints 44 and 46. The joint types for joints 44 and 46 may include revolute joints, prismatic joints, screw-type joints, or other joint types. Lower link 42 couples to load transmission point 32 at a distal end of lower link 42 opposite to upper link 40. Load transmission point 32 ultimately transfers load 14 through footwear 26 and footwear attachment 34 to the ground.

Upper link 40 includes one or more links or arms. Upper link 40 includes an actuator arm 50 and passive arm 52. Actuator arm 50 is disposed between load receptor point 30 and joint 44. Passive arm 52 is disposed between load receptor point 30 and joint 46. Passive arm 52 may include any suitable linkage, such as a tension cable, rigid member, or other linkage. In one embodiment, passive arm 52 comprises a stabilizing member. Load 14 is transferred from load receptor point 30 to lower link 42 through actuator arm 50 and joint 44 and through passive arm 52 and joint 46.

Actuator arm 50 includes a spring-based actuator 58 having structure-controlled stiffness. In one embodiment, spring-based actuator 58 includes a JackSpring™ Actuator, which further is described in U.S. Pat. Nos. 7,992,849 and 8,322,695, entitled Adjustable Stiffness Jack Spring Actuator, the entire disclosures of which are incorporated herein by reference. In another embodiment, spring-based actuator 58 includes any compliant actuator, spring-based actuator, or adjustable spring-based actuator. Where alternative spring-based actuators are used, the goal of the system is to behave like a compliant or spring supported structure while foot 28 is in contact with the ground during stance phase, and to allow free movement of the leg while foot 28 is in the air during swing phase.

Spring-based actuator 58 is a mechanical element based upon the concept of adding and subtracting coils from a spring. Spring-based actuator 58 is configured to accept load 14 though load receptor point 30 and subsequently dissipate the energy stored in the spring by using an actuator. Further, spring-based actuator 58 is uni-directional, such that spring-based actuator 58 assists user 12 in a first direction, while providing no support or resistance in an opposite direction. By providing uni-directional support, spring-based actuator 58 supports load 14 during stance phase, while swing phase remains unencumbered by spring-based actuator 58. One or more links of load support assembly 10 alternately couple and decouple with spring-based actuator 58 to provide uni-directional support during gait.

Lower link 42 is pivotally coupled to upper link 40. Lower link 42 may be a fixed-length rigid linking member, or may include a prismatic link or other joint. Lower link 42 optionally includes a compliant member, active member, or a combination of compliant and active members to assist user 12 with gait while wearing load support system 10. Lower link 42 together with upper link 40 comprise a link assembly. Load support system 10 includes a link assembly and a spring-based actuator 58 disposed on each side of load 14 and user 12.

Spring-based actuator 58 allows load support system 10 to be optimally tuned for varying loads 14 carried by user 12. The stiffness of load support system 10 is adjustable such that the system may be mechanically tuned. In one embodiment, the stiffness of load support system 10 is controlled or tuned using spring-based actuator 58. Load support system 10 accommodates various weights of load 14. Tuning of the effective stiffness of the system improves dynamic support for various load levels.

A sensor or sensor system 60 is worn by user 12. In one embodiment, sensor 60 is worn on each leg 62 of user 12. Sensor 60 may be disposed on an ankle, thigh, foot, or other part of user 12. Sensor 60 detects a physical state of user 12. The physical state measured by sensor 60 includes a kinematic state, a loading state, or a kinematic state and a loading state of user 12.

Load support system 10 further includes a controller or control system 64. Control system 64 is coupled to spring-based actuator 58. Measurements from sensor 60 are used by a control system 64 to control spring-based actuator 58. Control system 64 may also be used to control one or more compliant elements, motors, or active compliant members. Control system 64 uses the physical state measurement from sensor 60 to determine when user 12 is in the stance phase of gait and swing phase of gait. Control system 64 positions spring-based actuator 58 according to the user's physical state or phase of gait. When the user's foot is planted on the ground during stance phase, spring-based actuator 58 is positioned to receive a force, such as from gravitational load 14. Load 14 is transmitted from load receptor point 30 to load transmission point 32 into footwear 26 and footwear attachment 34 and to the ground. When control system 64 determines that the user's foot is lifted off the ground, during swing phase of gait, control system 64 positions spring-based actuator 58 to dissipate energy stored in spring-based actuator 58. During swing phase, load 14 is no longer transmitted from load receptor point 30 to load transmission point 32. Further, upper link 40, lower link 42, and spring-based actuator 58 are configured for uni-directional support. Load support system 10 supports load 14 during stance phase, but is configured for swing phase to be unencumbered by load support system 10. Because user 12 moves independently of load support system 10, control system 64 senses the kinematic motion of user 12 to determine the user's intent. Control system 64 uses the physical state measurement from sensor 60 to control spring-based actuator 58. Based on the physical state measurement, control system 64 positions spring-based actuator 58 according to the user's gait. User 12 moves without experiencing drag from load support system 10.

Control system 64 is a continuous function relating the position of spring-based actuator 58 to a measured signal. The continuous nature of control system 64 eliminates decision making by the system, if-then logic, and changes in state. By measuring kinematic or loading states, control system 64 adapts to changes in gait. In one embodiment, a processor of control system 64 operates at 1000 Hz. Control system 64 continuously calculates an output, rather than waiting on a gait event to trigger an output. Because the measured signal and output are related by a continuous function, the output is smooth. The measured signal is phase locked to the user's gait, and thus, the output of control system 64 is phase locked to the user's gait rather than time based. Because control system 64 is not time-based, control system 64 better adapts to changes in gait.

FIGS. 2 a-2 d show schematic representations of gravitational load support systems. FIG. 2 a shows a schematic representation of load support system 10, which supports gravitational load and allows for substantially unencumbered gait. Load support system 10 includes at least four linkages: lower link 42 and upper link 40 positioned on each side of load 14. A weight of gravitational load 14 is depicted by the center of gravity 70 of load 14. Weight is transmitted from load 14, through load receptor point 30, upper link 40, lower link 42, and load transmission point 32 to the ground.

FIG. 2 b shows further detail of a schematic representation of load support system 10. The attachment point for load 14 is shown at load receptor point 30, which is near a center of gravity 70 of load 14. Placement of load receptor point 30 near center of gravity 70 allows an effective spring mechanism 72 of load support system 10 to support the majority of the vertical load imposed on user 12. Placement of load receptor point 30 in a position behind upper torso 18 of user 12 and behind center of gravity 70 of load 14 causes load 14 to rotate forward and gently press into the back of the user's upper torso. Upon proper adjustment, a user feels little or no load at an upper torso 18 attachment point. In one embodiment, the attachment point for load 14 is shoulder area 22 where the load 14 is coupled to user 12 using straps 20 of backpack 16.

The effective structure of load support system 10 is represented by an effective spring 72. While a user's foot 28 is substantially stabilized on a surface, during stance phase, the system behaves like a passive spring. Effective spring 72 of load support system 10 operates in parallel with the user's leg 62. Load 14 bypasses user 12 and is directed through load support system 10 into the ground. Effective spring 72 shows how load support system 10 acts as a spring during stance phase to absorb gravitational load 14. As a user's foot 28 lifts into swing phase, effective spring mechanism 72 is driven out of the way of the actuator motor in spring-based actuator 58, allowing for fluid encumbered walking motion by user 12.

FIG. 2 c also shows schematically, with respect to FIG. 2 b, the vectors and moments that result during usage of load support system 10. An effective force F_(e) of load support system 10 is shown directed into load receptor point 30. The effective force F_(e) of load support system 10 has vertical and horizontal force components F_(g) and F_(x) shown at load receptor point 30. The force vectors show that a gravitational load L_(g) of load 14 is supported by the effective spring 72 having an effective force F_(e). A moment M₃₀ is created at load receptor point 30. Load support system 10 can be positioned such that load receptor point 30 is selected to minimize moment M₃₀ in order to reduce the rotation of load 14 into the user's upper torso 18. In addition, positioning of upper link 40 and lower link 42 and attachment points 30 and 32 relative to joints of user 12 eliminates the need for motors about the hip area of user 12.

FIG. 2 d shows schematically, the vectors and moments that result at ankle joint 80 during usage of load support system 10. Load transmission point 32 is positioned behind a user's ankle axis of rotation or ankle joint 80 to provide for balance and comfort. Where load transmission point 32 is located behind the ankle joint 80, the weight of the transmitted load adds weight at the heel of foot 28. The weight at the heel of foot 28 holds the user's heel down until user 12 is about to transfer to the opposite foot. The heel pinning effect causes improper heel rise timing during gait. The heel pinning effect is corrected by the use of torsional stiffness at load transmission point 32 or the point of rotation. A tuned and adjusted spring at or near ankle joint 80 is used to support load 14 and provide proper timing of heel rise, and reduce pinning of the heel.

Other components may also be added to load support system 10 to improve gait timing and proper heel rise. A component added for heel rise is selected to produce a force F_(s), which acts on the heel of foot 28 producing a moment M₈₀ at ankle joint 80. For example, a compliant element, an active element, or a combination of compliant and active elements are incorporated into load support system 10 or separately coupled to user 12 to assist with gait. In one embodiment, a compliant element, such as a spring, is coupled in proximity to load transmission point 32, foot 28, or lower link 42 to facilitate heel rise. In another embodiment, an active compliant device is coupled to foot 28 or lower link 42 to facilitate heel rise.

FIGS. 3 a-3 c shows a comparison of a user carrying a load with and without a load support system. Load support system 10 was tested with a user walking under three conditions: unleaded, loaded unassisted, and loaded assisted. FIG. 3 a shows user 12 walking without carrying load 14 in an unloaded state. Line 90 shows the relative position of a user's limbs and joints in the unloaded state. User 12 has a normal posture with upper torso 18 situated over hip joint 92, knee joint 94, and ankle joint 80. The gait of user 12 walking at a controlled pace in the unloaded state was analyzed as a control for comparison with the loaded states shown in FIGS. 3 b-3 c.

FIG. 3 b shows a user carrying a load without a load support system. User 12 is shown carrying a heavy load 14 in an unassisted loaded state. In one embodiment, user 12 was tested carrying a 36 kilogram (kg) load. The tested load included the weight of spring-based actuator 58, backpack 16, straps 20, and batteries. The posture and gait of user 12 changes to support the weight of load 14 and to stabilize user 12 while walking. User 12 leans forward to position the user's center of gravity for stability. Upper torso 18 is rotated forward. Load 14 is supported by shoulder area 22, upper torso 18, legs 62, hip joint 92, knee joint 94, ankle joint 80, and feet 28. Line 96 shows the orientation of the user's upper torso 18 leaning forward to adjust for load 14. The gait of user 12 walking at the controlled pace in a loaded unassisted state was analyzed. During testing, user 12 in the loaded unassisted state experienced stress that made conversation difficult for user 12, and carrying the unassisted load was the user's primary focus.

FIG. 3 c shows a user carrying a load while using a load support system. In one embodiment, user 12 was tested carrying the same load as in FIG. 3 b, a 36 kg load, and walking at the same controlled pace as in FIGS. 3 a-3 b, but with the added assistance of load support system 10. FIG. 3 c shows user 12 in an assisted loaded state, wearing heavy load 14 with backpack 16 and wearing load support system 10. The posture and gait of user 12 wearing load 14 assisted by load support system 10 is more similar to natural, unloaded gait condition shown in FIG. 3 a than to the unassisted loaded condition, shown in FIG. 3 b. Line 98 shows that user 12 does not rotate upper torso 18 forward as far as when in the unassisted loaded state. The user does not need to shift the user's center of gravity as far forward, because a majority of load 14 bypasses the user's body though load support system 10.

Load support system 10 is coupled to the user's upper torso 18, using straps 20 of backpack 16. Other suitable attachment mechanisms may be incorporated into load support system 10 to couple the system to user 12. Load support system 10 further includes upper link 40 pivotally coupled to lower link 42. Upper link 40 is coupled to load receptor point 30 on backpack 16. Lower link 42 is coupled to footwear 26, such as shoes or boots worn by user 12, by an attachment device. As user 12 walks, load support system 10 transfers the load 14 into load transmission point 32 on footwear 26 and into the ground, thereby bypassing the user's lower body.

During testing, the gait of user 12 walking at the controlled pace was analyzed. User 12 in the assisted loaded state showed a more natural and relaxed gait than the unassisted loaded state. The testing also included a 2-dimensional motion capture analysis, which captured images of the user walking under the assistance of the system. Visual markers placed at the foot 26, ankle 80, knee 94, and hip 92 were used to determine joint kinematics for the knee and ankle during an entire step. Results showed that load support system 10 allowed the wearer normal able bodied gait motion while wearing the 36 kg load. The results of the analysis show good correspondence of the ankle and knee motions in the loaded assisted state to that of an unloaded able bodied individual. Load support system 10 does not encumber gait, because the exoskeleton system structure does not attach to the anatomical limbs of user 12 and thus cannot force user 12 into any particular gait style. Rather, load support system 10 is designed to allow able-bodied gait to occur naturally even when carrying a significant load. In the tested embodiment, load 14 included a 23 kg weight plus the 13 kg weight of load support system 10. Load support system 10, however, is also designed to support weights greater than 23 kg. Load support system 10 is not limited to a specific maximum weight. Load support system 10 is scalable to support weights equivalent to the maximum load worn by a user. Load support system 10 is not limited to providing assistance during walking, but is programmable and reprogrammable to support other modes of gait, for example, inclines, stairs, and running.

FIG. 4 shows a tension spring-based actuator assembly used for load support system 10. Spring-based actuator 58 is a mechanical element that adds or subtracts active coils from a spring. Spring-based actuator 58 allows load support system 10 to be optimally tuned for varying loads 14 carried by user 12. For the purpose of power optimization, spring stiffness tuning is a desired attribute of spring-based actuator 58. In addition, spring-based actuator 58 for load support system 10 is further designed to be uni-directional. Spring-based actuator 58 provides support between load 14 and the ground, but will allow user 12 to swing each leg faster than the capability of spring-based actuator 58, or other motors or controls. In one embodiment, load support system 10 includes a tension spring-based actuation assembly 100. In another embodiment, load support system 10 includes a compression spring-based actuation assembly.

Tension spring-based actuation assembly 100 includes actuator arm 50 and passive arm 52 substantially parallel to actuator arm 50. Actuator arm 50 is disposed between load receptor point 30 and joint 44. Passive arm 52 is disposed between load receptor point 30 and joint 46. Actuator arm 50 includes spring-based actuator 58. Spring-based actuator 58 is an assembly including a tension cable 110 a spring actuation nut 114, and a spring 116.

Tension cable 110 couples to joint 46 and extends around a pulley 120 at load receptor point 30. In one embodiment pulley 120 includes a pulley belt arrangement with a 3:1 ratio. Tension cable 110 extends through a hollow portion of actuator arm 50 and couples to spring actuation nut 114. Tension cable 110 may include additional linkages, such as a turnbuckle, or other fasteners. Spring 116 includes a compliant coil spring disposed around actuator arm 50. Spring 116 interfaces with spring actuation nut 114. Spring actuation nut 114 is disposed between coils of spring 116. In one embodiment, spring actuation nut 114 includes threads, which fit between the coils of spring 116. In one embodiment, spring actuation nut 114 includes one or more pins, or one or more pins in radial bearings, or another nut configuration. Spring actuation nut 114 further couples to tension cable 110 through an opening, such as a slit, in actuator arm 50. Spring actuation nut 114 fits through the opening in actuator arm 50 to attach to tension cable 110 at an attachment point within actuator arm 50.

When user 12 is in stance phase, foot 28 is in contact with the ground. Load support system 10 using tension spring-based actuation assembly 100 receives load 14 at load receptor point 30. As the user's leg 12 moves through stance phase, lower link 42 rotates in direction d₄₂ as force is directed from load receptor point 30 through actuator arm 50 to joint 44 and into lower link 42. Passive arm 52 is pulled at joint 46 in direction d₄₆ causing tension in tension cable 110. When tension is applied to tension cable 110, tension cable 110 pulls on spring actuation nut 114 at the attachment point inside actuator arm 50.

As tension cable 110 pulls on spring actuation nut 114, spring actuation nut 114 acts on the active coils in spring 116. The deflection of spring 116 is in direction d₁₁₆. When spring 116 deflects, the energy of load 14 is stored in spring 116. The deflection of spring 116 allows load support system 10 to support load 14 during stance phase.

Spring-based actuator 58 further includes an actuator 130. Actuator 130 couples to spring 116 through a belt or gear assembly 132. In one embodiment, actuator 130 is a direct current motor operating at up to 8,000 revolutions per minute (RMP). Belt assembly 132 couples to spring 116 to drive a rotation of spring 116. Actuator 130 engages to rotate spring 116 to translate spring actuation nut 114 to reduce the number of active coils in spring-based actuator 58 and thereby dissipating the energy stored in the spring. Actuator 130 rotates spring 116 to drive slack into tension cable 110. The slack in tension cable 110 allows user to move into swing phase unencumbered by load support system 10. Spring-based actuator 58 may further include additional support structures, such as support cable 140.

Tension cable 110 is used to provide a uni-directional application of force to spring-based actuator 58. Thus, tension cable 110 provides a supporting force to the carried load in the upper link 40 when the user's foot 28 is on the ground during stance phase. Tension cable 110 also allows the user's leg 62 to effectively decouple from spring-based actuator 58 while in swing phase, thereby allowing leg 62 to move freely and unencumbered. A uni-directional actuator effect can be accomplished by tension or compression. In tension spring-based actuation assembly 100, compressive loading in spring-based actuator 58 system is ignored and not transmitted to the overall system. A reversed system, which uses compression rather than tension, operates using the same concepts as in tension spring-based actuation assembly 100. Load 14 is transferred into a spring, by either tension or compression, and an actuator drives the nut or the spring to dissipate the energy stored in the spring.

In an alternative embodiment, gravitational load support system includes a compression spring-based actuator assembly. The compression spring-based actuation assembly includes actuator arm 50 and passive arm 52 substantially parallel to actuator arm 50. Actuator arm 50 is disposed between load receptor point 30 and joint 44. Passive arm 52 disposed to load receptor point 30 and joint 46. Passive arm 52 is a rigid member, rather than a tension cable, and is pivotally coupled to lower link 42 at joint 46. Actuator arm 50 includes spring-based actuator 58. A portion of actuator arm 50 is configured to alternately couple and decouple with spring-based actuator 58. During stance phase, actuator arm 50 couples to spring-based actuator 58. During swing phase, actuator arm 50 decouples from spring-based actuator 58 by creating a gap between a portion of actuator arm 50 and spring 116 in spring-based actuator 58. The portion of actuator arm 50 extending from joint 44 temporarily decouples from spring 116 to provide substantially unencumbered motion as lower link 42 moves in a direction opposite to direction d₄₂.

In the compression configuration, spring-based actuator 58 is an assembly including a spring actuation nut 114, a spring 116. Similarly to the tension configuration, spring 116 is disposed along actuator arm 50 and interfaces with spring actuation nut 114. Spring actuation nut 114 is disposed between coils of spring 116 and couples to actuator 130.

When user 12 is in stance phase, load support system 10 using compression spring-based actuation assembly receives load 14 at load receptor point 30. As the user's leg 12 moves through stance phase, lower link 42 pivots at joint 46 and rotates in direction d₄₂. As lower link 42 moves in direction d₄₂, actuator arm 50 is compressed. Actuator arm 50 pushes on spring 116 to compress spring 116. As actuator arm 50 compresses spring 116 against spring actuation nut 114, the coils in spring 116 that are disposed between spring actuation nut 114 joint 44 compress. When spring 116 is compressed, the energy of load 14 is stored in spring 116 and load support system 10 supports load 14 during stance phase.

In the compression configuration, spring-based actuator 58 further includes an actuator 130. Actuator 130 couples to spring 110 through a belt or gear assembly 132. Gear assembly 132 couples to spring actuation nut 114 to drive a rotation of spring actuation nut 114. Actuator 130 engages to rotate spring actuation nut 114 to translate spring 116 to reduce the number of active coils in spring-based actuator 58 and thereby dissipating the energy stored in spring 116. Actuator 130 drives spring 116 away from actuator arm 50 to decouple actuator arm 50 from spring 116. The decoupling of actuator arm 50 from spring 116 creates a gap along actuator arm 50, between joint 44 and spring 116, that allows user 12 to move into swing phase unencumbered by load support system 10.

A compression spring-based actuation assembly provides a uni-directional application of force in load support system 10. Thus, spring-based actuator 58 provides a supporting force to the carried load in the upper link 40 when the user's foot 28 is on the ground during stance phase. Spring-based actuator 58 also allows the user's leg 62 to effectively decouple from spring-based actuator 58 while in swing phase, thereby allowing leg 62 to move freely and unencumbered. A uni-directional actuator effect can be accomplished by tension or compression.

FIGS. 5 a-5 b show schematic diagrams of coils in a spring-based actuator used for a load support system. FIG. 5 a shows a position of a spring-based actuator having a region of active coils defined by a nut. Spring-based actuator 58 includes a helical or coil spring 116 where the number of active coils 154 is adjustable by rotating spring 116, or alternatively, by rotating spring actuation nut 114. Spring-based actuator 58 is comparable to a lead screw. The lead and pitch for spring-based actuator 58 are variable based upon an imposed axial force F_(a). Active coils 154 are defined by a position of spring actuation nut 114. A position of spring actuation nut 114 is indicated by line 152. Inactive coils 150 are shown in a position opposite spring actuation nut 114 from active coils 154. As spring 116 or spring actuation nut 114 rotates, the number of active coils 154 changes. In one embodiment, the spring 116 translates along the length of actuator arm 50 to change the number of active coils 154.

FIG. 5 b shows a position of a spring-based actuator having a region of fewer active coils than the position shown in FIG. 5 a. The stiffness of a coiled spring is a function of geometry, material, and number of active coils, such as active coils 154. In most springs, the stiffness K_(s) of the spring is fixed. For spring-based actuator 58, however, the number of active coils 154 is adjusted and thus the stiffness K_(e) of the mechanism is adjusted. In FIG. 5 b, the position of spring actuation nut 114 and spring 116 shows fewer active coils 154 available to do work, causing spring-based actuator 58 to have less stiffness than where fewer active coils 154 are available.

Spring-based actuator 58 offers a combination of compliance, energy storage, and actuation. In addition, because spring-based actuator 58 acts similarly to a lead screw system, a lightweight gearbox is built-in to the system. The adjustability of the position and stiffness of spring 116 allows spring-based actuator 58 to include properties of energy storage or energy dissipation. Energy storage is achieved during spring 116 loading. Energy dissipation is achieved by allowing spring 116 to absorb a load or axial force F_(a) and then drive the spring backwards so that spring 116 does not return that stored energy to the environment.

The lead of spring-based actuator 58 is a function of force F_(a), and the stiffness K_(e) of the device is a function of the number of active coils 154. The functions related to the response of actuator 130 are defined on a per coil basis. For example, the deflection of actuator 130 is defined in terms of the deflection of a single coil, rather than overall unit length change.

$\begin{matrix} {\tau = {\frac{\beta \cdot l_{o}^{2}}{2\pi} \cdot \left\lbrack {\left( \frac{l}{l_{o}} \right)^{2} - \frac{l}{l_{o}}} \right\rbrack \cdot \frac{l}{l_{o}} \cdot \left\lbrack \frac{\frac{l}{l_{o}} + {\mu \; \cot \; \alpha_{o}}}{1 - {{\mu \cdot \frac{l}{l_{o}}}\tan \; \alpha_{o}}} \right\rbrack}} & (1) \end{matrix}$

Where: τ=actuator torque

-   -   β=spring stiffness of a single coil     -   l=spring lead     -   l_(o)=spring un-deflected lead     -   α=lead angle     -   μ=offset variable

Equation (1) describes the torque necessary to be applied to spring-based actuator 58 in order to achieve a lifting load. The load or force in equation (1) is captured by the ratio l/l_(o), which is the deflection of spring 116. The variables l and l_(o) represent the lead of spring 116 and the un-deflected lead of spring 116 respectively, and β represents the single coil spring stiffness. The remaining terms in equation (1) are used to develop the resulting friction influence. Equation (1) is applied to the specific geometry of the linkages in load support system 10. The relationships are combined with normal, able-bodied gait dynamics, and a resulting tuned control pattern is developed, as shown in a graph in FIG. 6.

FIG. 6 shows a graph of a spring-based actuator control pattern. Line 164 shows a tuned path of control pattern for spring-based actuator 58. In the early part of stance phase, known as load acceptance, spring-based actuator 58 drives to increase the total number of active coils 154 engaged in spring 116. As the number of coils in a spring is inversely proportional to stiffness, increasing the coil count has an effect of reducing the stiffness of the spring, such that spring 116 feels softer. However, in spring-based actuator 58 there exists a coupling between stiffness and actuator 130 displacement. Although the stiffness decreases, the amount of load acceptance increases.

Line 166 shows a selected control pattern developed based on the calculated control pattern in line 164. Line 166 represents the control path used for load support system 10 for walking. The difference between the control pattern in line 164 and the control pattern in line 166 is that the initial active coil count of spring 116 is held as a constant for nearly half of the walking gait cycle in line 166, the majority of the stance phase. Thus, for the first half of a step, actuator 130 remains off and the passive properties of spring 116 are engaged as shown by line 166. During the second half of the walking gait cycle, actuator 130 activates to support leg movement during the swing phase of gait. To support uni-directional actuation, load support system 10 does not prevent user 12 from stepping out farther or faster than actuator 130 can drive. The uni-directional actuator behavior allows an unencumbered swinging motion of the leg, and also allows user 12 to accomplish a greater stride, to compensate for obstacles in the path, such as potholes, branches, or any other walking hazard. The goal of load support system 10 is to support the load while the foot is on the ground while permitting as much freedom of movement of the leg as possible while the foot is in the air.

FIGS. 7 a-7 b show a graph of kinematic results measured from a user wearing a gravitational load support system. FIG. 7 a shows a graph comparing the kinematics of the ankle for able-bodied gait and loaded assisted gait. Line 170 shows ankle angle kinematics during one gait cycle for unloaded able-bodied gait. Line 172 shows ankle angle kinematics during one gait cycle for user 12 wearing load 14 and load support system 10. Line 172 shows that the kinematics of the ankle while using load support system 10 to support load 14 is similar to the kinematics of the ankle while user 12 is not wearing load 14, shown by line 170.

FIG. 7 b shows a graph comparing the kinematics of the knee for able-bodied gait and loaded assisted gait. Line 176 shows knee angle kinematics during one gait cycle for unloaded able-bodied gait. Line 178 shows knee angle kinematics during one gait cycle for user 12 wearing load 14 and load support system 10. Line 178 shows that the kinematics of the knee while using load support system 10 to support load 14 is similar to the kinematics of the knee while user 12 is not wearing load 14, shown by line 176. Line 178 shows that without a compliant element added during heel rise, the knee joint is slightly hyperextended. A compliant element, or spring, is added to load support system 10 to improve the timing of a user's gait and prevent joint hyperextension.

FIG. 8 shows a schematic diagram of an alternative load support system. In load support system 10, the weight of the transmitted load adds weight at the heel of foot 128. The weight at the heel of foot 128 holds the user's heel down until user 12 is about to transfer to the opposite foot. The heel pinning effect causes improper heel rise timing during gait. The heel pinning effect is corrected by the use of torsional stiffness at load transmission point 32 or the point of rotation. For example, a compliant element, an active element, or a combination of compliant and active elements are incorporated into load support system 10 or separately coupled to user 12 to assist with gait. In one embodiment, a compliant element 190, such as a spring, is coupled to lower link 42 and to foot 128 at attachment point 192. As the user's leg rolls forward during stance phase, compliant element 190 is compressed. As user 12 begins heel rise, the energy stored in compliant element 190 is released and facilitating proper heel rise timing. Compliant element 190 is tuned and adjusted according to the user and to the weight of load 14. In one embodiment, compliant element 190 includes a torsional spring, a leaf spring, a cable having elastic properties, or another type of compliant device.

In another embodiment, an active compliant device 196 is coupled to load transmission point 32 and the user's leg, or other fixed point to facilitate heel rise. Active compliant device 196 includes a spring 200 and actuator 202 to add energy to the user's heel rise. Active compliant device 196 comprises a robotic ankle joint worn by user 12. In one embodiment, active compliant device 196 couples to a user's lower leg or other fixed point 204. Actuator 202 may be used to tune spring 200 and to add power to gait. Actuator 202 may be controlled by control system 64 or similar system to position actuator 202 according to the user's physical state or phase of gait. Compliant element 190 and active compliant device 196 operate to produce a moment or torque at ankle joint 80. The moment produced at ankle joint 80 assists with movement of the user's foot in the direction of plantar flexion. Compliant element 190 or active compliant device 196 operates to improve the user's gait while user 12 wears load support system 10.

FIGS. 9 a-9 d show a graph of the relationship of motor power consumption to percentage of a gait cycle during use of a gravitational load support system. FIG. 9 a shows the relationship of active coils in spring-based actuator 58 with respect to the percentage of gait cycle. During stance phase for the first 50-60% of a gait cycle, load support system 10 accepts load 14 and spring-based actuator 58 is positioned with a high number of active coils 154. Line 210 represents the number of active coils 154 in spring-based actuator 58 with a calculated control pattern. During swing phase for the remaining 40-50% of the gait cycle, the number of active coils 154 is decreased by actuator 130.

FIG. 9 b shows the relationship of motor power consumption in relation to percentage of gait cycle for the calculated control pattern shown in FIG. 9 a. In FIG. 9 b, line 212 represents the power required from a motor to produce an actuator power shown by line 214. When the number of active coils is increased using actuator 130 in spring-based actuator 58, the power required from the motor peaks early in the gait cycle. When actuator 130 decreases the number of active coils in spring-based actuator 58, the power required from the motor peaks again during swing phase. The motor requirements from FIG. 9 b are used to optimize the performance of spring-based actuator 58.

FIG. 9 c shows the relationship of active coils in spring-based actuator 58 with respect to the percentage of gait cycle using an alternative control pattern. Line 220 represents the number of active coils 154 in spring-based actuator 58 with a selected control pattern. During stance phase, the first 50-600 of a gait cycle, load support system 10 accepts load 14 and spring-based actuator 58 holds the number of active coils 154 constant. During swing phase, the number of active coils 154 is decreased by actuator 130.

FIG. 9 d shows the relationship of motor power consumption in relation to percentage of gait cycle using an alternative control pattern shown in FIG. 9 c. In FIG. 9 d, line 222 represents the power required from a motor to produce an actuator power shown by line 224. The motor requirements depicted in lines 222 and 242 are used to optimize the performance of spring-based actuator 58.

Further, the relationship torque and motor speed in spring-based actuator 58 performance shows that high speed motion may exceed the maximum threshold of an 8,000 rpm motor. In one embodiment, actuator 130 for spring-based actuator 58 includes an RE-40 motor and has a maximum speed of 8,000 rpm. The maximum speed of an RE-40 motor increases as torque decreases. Even where motor torque is reduced and motor speed is maximized, a user may move faster than the motor is capable of rotating. Where a user exceeds motor speed, the user feels drag or resistance from the motor. However, in load support system 10, where the user moves faster than the motor, the decoupling of spring-based actuator 58 prevents user 12 from feeling resistance from actuator 130. The uni-directional spring-based actuator 58 allows load support system 10 to operate faster than the maximum speed of actuator 130, when user 12 drives the system during swing phase. Actuator 130 is designed to maximize overall torque utilization, which has an effect of maximizing its overall operational efficiency.

Thus, gravitational load support systems are disclosed. While embodiments of the present invention have been shown and described, it will be apparent to those skilled in the art that many more modifications are possible without departing from the inventive concepts herein. Moreover, the testing examples described herein are representative only and are not to be construed as limiting. The invention, therefore, is not to be restricted except in the spirit of the following claims.

While one or more embodiments of the present invention have been illustrated in detail, the skilled artisan will appreciate that modifications and adaptations to those embodiments may be made without departing from the scope of the present invention as set forth in the following claims. 

What is claimed:
 1. A method of making a load support device, comprising: providing a first link coupled to a load; providing a second link configured to couple to a footwear, the second link pivotally coupled to the first link; disposing a first compliant member between the load and the second link; coupling a first actuator to the first compliant member to control a stiffness of the first compliant member; and providing a control system to control the first actuator based on a gait activity.
 2. The method of claim 1, further including coupling a second compliant element to the footwear.
 3. The method of claim 1, further including coupling a second actuator to the footwear.
 4. The method of claim 1, further including tuning the load support device based on the load.
 5. The method of claim 1, further including providing a sensor configured to couple to a user to measure a physical state of the user.
 6. The method of claim 5, further including actuating the first actuator based on the physical state of the user.
 7. A method of making a load support device, comprising: providing a first link coupled to a load; providing a second link configured to couple to a footwear, the second link pivotally coupled to the first link; disposing a first compliant member between the load and the second link; and coupling a first actuator to the first compliant member to control a stiffness of the first compliant member.
 8. The method of claim 7, wherein the first compliant member includes a tension spring or a compression spring.
 9. The method of claim 7, further including coupling a second compliant member to the footwear.
 10. The method of claim 7, further including coupling a second actuator to the footwear.
 11. The method of claim 7, wherein the first compliant member and first actuator are configured to provide uni-directional support for gait.
 12. The method of claim 7, further including: providing a sensor configured to couple to a user to measure a physical state of the user; and actuating the first actuator based on the physical state of the user.
 13. The method of claim 7, further including tuning the load support device based on the load.
 14. A load support device, comprising: a first link configured to couple to a load; a second link configured to couple to a footwear and the first link; a first compliant member disposed between the load and the second link; and a first actuator coupled to the first compliant member to control a stiffness of the first compliant member.
 15. The load support device of claim 14, wherein the first compliant member further includes a helical spring.
 16. The load support device of claim 14, wherein the first link includes a tension cable coupled to the first compliant member.
 17. The load support device of claim 14, wherein the first compliant member includes a tension spring or a compression spring.
 18. The load support device of claim 14, further including a second compliant member coupled to the footwear.
 19. The load support device of claim 18, further including: a sensor configured to obtain a physical state measurement; and a control system coupled to the sensor and first actuator, wherein the control system is configured to produce a command to control the first actuator based on the physical state measurement.
 20. A load support device, comprising: a link assembly configured to couple to a load and to a footwear; a first compliant member coupled to the link assembly between the load and the footwear; and an actuator coupled between the load and the footwear, the first compliant member and actuator configured to dissipate the load during gait.
 21. The load support device of claim 20, wherein the first compliant member further includes a helical spring.
 22. The load support device of claim 20, wherein the link assembly further includes a tension cable coupled to the first compliant member.
 23. The load support device of claim 20, wherein the first compliant member includes a tension spring or a compression spring.
 24. The load support device of claim 20, wherein the actuator is configured to control a stiffness of the first compliant member.
 25. The load support device of claim 20, further including a second compliant member coupled to the footwear. 